Energy drinks such as Red Bull and Monster are the hottest-selling component of the beverage industry, but medical experts are sounding the alarm about the possible health hazards they pose and calling for better regulation.

Last month, the concern reached Congress, where members took energy-drink makers to task for marketing they say is targeted at children and teens, marketing that seems particularly unsettling given a number of recent deaths of teens linked to the consumption of the caffeinated drinks.

"I find the denial of marketing to children difficult to accept," Sen. Richard Blumenthal, D-Conn., a member of the Senate commerce committee, said at the July 31 hearing about ads that show bikini-clad girls and extreme skateboarders with energy drinks. "The facts and common sense show that the pitches and promotions to kids have been open and relentless."

A few days later, the Institute of Medicine convened a meeting of medical experts to examine what exactly is known about safety issues involving energy drinks. The institute will report its findings and recommendations to the Food and Drug Administration.

Houston cardiologist Dr. John Higgins, a meeting participant who has conducted research on the drinks, said the experts agreed more investigation is needed but added that studies suggest the drinks are harmful to those younger than 18; may be associated with risk-taking behavior as well as college-student consumption of alcohol and nonprescription drugs; and have unique effects on the body and brain that suggest the importance of the mix of caffeine and other ingredients.

"It's not just the caffeine in the drinks," says Higgins, a professor at the University of Texas Health Science Center at Houston. "It appears that the interaction of caffeine, sugars and vitamins creates a whole different beast, a whole new pharmaco-dynamic."

Higgins demonstrated some of the heart hazards of energy drinks. In a July paper in the International Journal of Cardiology, he reported his cardiac blood vessels became sluggish and didn't open as well after he drank a 24-ounce can of Monster, compared to their pre-consumption function. He more recently began a study to evaluate the effect of energy drinks on the heart function of 50 healthy University of Texas medical students.

Despite increasing concerns, there's no denying the drinks' growing popularity. In 2012, their U.S. sales topped $10 billion, more than is spent on iced tea or Gatorade. According to the Beverage Marketing Corporation, the average American drank 1.2 gallons of energy beverages in 2010.

Energy drinks typically contain 10 to 15 milligrams of caffeine per ounce, or between 160 and 240 milligrams in a 16-ounce can, which manufacturers like to point out is less than is in a coffeehouse cup of coffee. They're less likely to volunteer that that's five times more caffeine than is in a soft drink, that people drink coffee at a much slower rate than an energy drink and that most teenagers have drunk too little coffee to have adjusted to its effects.

Other energy-drink ingredients, mostly stimulants, include undisclosed amounts of the amino acid taurine, herbs such as ginseng or guarana, vitamin B and something called glucuronolactone, which is related to a kind of sugar. Experts have called for manufacturers to list exact amounts on labels.

The mix has proved so potent that the Food and Drug Administration has posted adverse-event reports linked to the drinks that include five deaths, 53 illnesses and two lasting disabilities. The administration has not determined the drinks caused the harm, but the autopsy report of a 14-year-old girl who died after drinking two 24-ounce Monster beverages within 24 hours listed caffeine toxicity as the cause of death.

Chris Gindlesperger, spokesman for the American Beverage Association, denies any relationship between energy drinks and the deaths. He called energy drinks safe and stressed that claimants need to take into account the health of the person and what else he or she had consumed lately.

Certainly, the pressure's building on the energy-drink industry. The American Medical Association has called for a ban on advertising to anyone younger than 18, the Food and Drug Administration continues to investigate possible health hazards, Congress is considering intervening, and wrongful-death lawsuits have been filed.

"The cases that have been reported are the tip of the iceberg," Higgins, the cardiologist, said. "I don't recommend energy drinks to anyone under 18, pregnant women and those known to be sensitive to caffeine and, until we've done more research into it, I think everyone else should limit their intake to no more than one can in any 24-hour period."